Watercraft speed sensor

ABSTRACT

A sensor for measuring movement of an object relative to a fluid has a housing fixed to a surface of the object and a spring on the housing formed by a plurality of blades each having an outer end fixed to the housing and an inner end connecting to a hub, with the plurality of blades defining a plane. Respective strain gauges are carried on the blades. A rigid pin is mounted on the hub of the spring, extends in a direction generally perpendicular to the plane, and projects from the surface of the object and into the fluid.

FIELD OF THE INVENTION

The present invention relates to a speed sensor. More particularly this invention concerns a device for detecting the speed of a vehicle in a fluid, in particular a watercraft in water.

BACKGROUND OF THE INVENTION

The invention pertains to a sensor for measuring a movement of an object relative to a fluid. In particular the invention pertains to a sensor that permits sensing of a movement of an object, which is a watercraft, like a surfboard, a boat, a yacht, a canoe, or any other watercraft.

The sensor of the invention also includes submarine applications, such as diving watercraft.

Further the sensor according to the invention can be configured to sense movements of objects, such as vehicles, in fluids other that water, for example in air or in gases.

It is important that the invention not only serves for measuring movement of the object in the fluid but also comprises sensors for sensing movement of a fluid relative to the water.

For example the sensor according to the invention is capable of sensing movements of fluids, as kerosene or fuel or other combustible, relatively to a fixed container or tank that receives this fluid, for example for monitoring a required mixing of different parts of a fluid.

In nautical applications there have been described different systems and sensors to measure movements of an object in the water. For example it is often desirable to obtain speed information or wind information.

Known Prior Art

U.S. Pat. No. 7,737,923 discloses a device serves for measuring a fluid flow.

U.S. Pat. No. 7,166,005 discloses a sensor having a spherical lobe.

US 2009/0042467 discloses a speed meter.

DE 197 18 917 discloses a sensor having at least two optical detectors that are detecting air bubbles in the water flowing along the two detectors.

U.S. Pat. No. 6,213,041 discloses a speed sensor that comprises of a rotator that includes a plurality of blades. The speed sensor also includes a rotation detector to determine the rotational speed of the rotator.

DE 33 19 684 describes a propeller to be dispensed in water. The rotational speed of the propeller corresponds to the speed of the object in water.

DD 227 329 discloses detecting fluid movement measurements. The sensor proposed by this document uses heated electric lines.

DE 85 23 456.7 [U.S. Pat. No. 4,653,319] discloses a detection sensor for speed measurements for watercraft comprising a magnet and four electrodes.

The prior-art sensors use various sensors and technical features for measuring movements but mostly employ moving parts. This is of disadvantage as such parts can deter and also can be blocked for any unforeseen reasons.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved motion sensor.

Another object is the provision of such an improved motion sensor that overcomes the above-given disadvantages, in particular that is reliable and does not employ moving parts.

SUMMARY OF THE INVENTION

According to the invention a sensor is provided for measuring movement of an object relative to a fluid. The movement that can be sensed can be a 3-dimension (3D) or 2D-movement. In particular, the sensor of the invention can provide information that describes relative movement of the object in the fluid or that permit information that describes a relative movement of the object in the fluid to be derived from the sensed data.

The movement detected can comprise information about the movement in x-, y- and/or z-direction, where x, y and z are directions in a Cartesian coordinate system.

The sensor of the invention is be fixed on the object, in particular at an outer face or near to an outer face of the object. The sensor comprises a housing that can be of any appropriate shape.

For example the housing can be recessed in a cavity of the object.

If the object is a watercraft, the housing will be preferably be mounted at a place on a surface that is, when the watercraft is used, in contact with the water.

Further preferably the housing is mounted flush to the surface of the object or recessed in the surface of the object, such that the housing does not project from the surface.

The housing of the sensor of the invention holds a spring. The spring has a plurality of blades, for example three, four or more blades. The blades are made of an appropriate elastically deformable material such as metal or plastic to generate the spring action of the blade.

Each blade has an outer end and an inner end. The outer ends of the blade are connecting to the housing directly or to an intermediate member such as a ring that can be part of the housing or can be fixed to the housing. The outer end of each blade is, when the sensor is mounted, fixed to the surface of the object. The inner ends of the blades are connecting to a hub of the spring.

A rigid pin is set in the hub of the spring. The pin according to the invention is an elongated member configured as a rod or a bolt and has an elongated shape. Preferably, the pin is cylindrical, further preferably having a circular cross section. However other cross sections are also comprised in the teaching of the invention. Further, the pin not necessarily needs to be cylindrical but also may have a shape varying along its axis.

The pin of the sensor according to the invention is rigid. The pin therefore is not significantly elastically deformable.

The array of blades defines a plane and/or approximates a plane. The pin extends in a direction of a normal vector to this plane, so the plane is perpendicular to this plane.

When the sensor is mounted at the object, the pin projects from the surface of the object.

The pin is, according to the invention, configured to dip down into the fluid in which the object is typically floating or immersed.

When the object is moving relative to the fluid, for example a surfboard is moving in the water, according to the speed of the object relative to the water there are forces exerted radially by the water onto the pin. The pin itself is rigid or stiff and will not change shape, but as one end of the pin is held by the hub of the spring and as the water exerts a force onto the free end of the pin, the pin will be slightly pivoted. The pin will pivot only for a very, very small angle, for example less than 1°. The force exerted by the water onto the pin will lead to a force exerted onto the spring. The pin will act as a force-transmitting member. The forces exerted against the pin will slightly deform the blades.

According to the invention a plurality of strain gauges are positioned on the blades. The deformation of the blades and their strain gauges, changes the resistance of the strain gauge.

The strain gauges are part of an electrical circuit and any change of the resistance of the strain gauge can be detected by the circuit.

By detecting the changes of the resistance or by detecting any electrical or physical measuring value that changes following a change of the resistance of the strain gauges, the force exerted by the fluid onto the pin can be calculated or derived and from the values not only the value of the force exerted on the pin can be measured and/or calculated but also the direction of the force exerted onto the pin can be measured and/or calculated.

According to an advantageous embodiment of the invention there are at least three blades, each having a respective strain gauge. Appropriately positioning the blades and their strain gauges and integrating the strain gauges into an electric circuit allows a measurement of the speed and/or the orientation of the relative forces to be performed.

According to an advantageous embodiment of the invention the plurality of blades comprises at least three blades. This embodiment provides a sensor with a construction using a minimum number of blades and requires a minimum number of strain gauges.

According to a further advantageous embodiment of the invention the blades are arranged angularly equidistant from each other. Between each pair of blades the same angular distance is provided. This provides a sensor that permits use of known electronic circuit and facilities calculation of the forces applied to the pin.

According to a further advantageous embodiment of the invention the plurality of strain gauges comprises at least three strain gauges each positioned on a respective one of three different blades. This embodiment enables provision of a sensor using a minimum number of strain gauges.

According to a further advantageous embodiment of the invention the pin supports a float. A float may be configured as a ring like member or a disk like member and may be positioned on the pin, for example at the free lower end of the pin. The float can detect forces in a direction along the longitudinal axis of the pin. This direction is in this patent application also designated the z-direction.

In measuring these forces exerted onto this pin in that direction that is parallel to the pin's normally vertical axis, a real 3-dimension (3D) measurement value can be obtained and delivered to a user or to a spectator as further information. As an alternative of using a float, a membrane or any other pressure sensitive element can be used to detect movements of the pin in the vertical z-direction or to detect movements of the object in z-direction relative to the fluid. This membrane can for example be positioned at the end of the pin, or can be positioned alternatively at the spring or near to the spring, in particular inside the housing. The membrane can detect differences in pressure from which a movement of the object in z-direction relative to the fluid can be derived by calculation.

According to a further advantageous embodiment of the invention the housing comprises a cover mounted in flush arrangement to the surface of the object. This embodiment provides a sensor that will practically not disturb movement of the object in the fluid as there are, besides the pin, no parts or element of the sensor projecting from the surface of the object.

According to a further advantageous embodiment of the invention the cover has a bore having an inner diameter larger than the outer diameter of the pin. The cover therefore with its bore surrounds the pin but permits slight radial movement of the pin, avoiding any contact between the pin and the cover to not generate incorrect measurements.

According to a further advantageous embodiment of the invention the spring assumes a rest position for the pin that is reached when no forces act upon the pin. The spring will permit pivoting of the pin relative to the housing when forces are exerted by the fluid upon the pin but will reposition the pin into the rest position as soon as the forces exerted on the pin are lifted.

According to the invention the sensor has a housing mounted in fixed arrangement relative to the surface of the object, the housing holding a base. The base is fixed to the housing.

The base comprises a hub having an elastically deformable pin. A plurality of strain gauges are positioned on the pin. When a force is applied onto the pin, the pin will deform elastically or bend. Bending for small angles is sufficient. Strain gauges are positioned on the pin and will change their resistance when the pin bends even slightly. Again, the strain gauges are parts of an electrical circuit, and the change in resistance of the strain gauges due to a bending of the pin can be sensed or detected.

To avoid positioning the strain gauges in the fluid the pin can consist of several concentric elements, including one or more hollow pipes. The strain gauges can be positioned on the outer face of an inner pin and an outer pipe can be configured to be hollow and is put over the inner pin to protect the strain gauges.

The system comprises a sensor as described above and a first communication unit on the object. The first communication unit is connected to the sensor, either by cable or by wireless connection. The first communication unit can also be arranged within the housing.

This system further comprises a second communication unit that can receive information from the first communication unit. The information can be transmitted using any kind of electromagnetic waves of any appropriate frequency and wave length using any kind of protocol. Further alternatively acoustical or optical waves can be transmitted for connecting the first communication unit with the second communication unit. Preferably, radio frequency signals will be transmitted between the first communication unit and the second communication unit.

Further preferably the second communication unit is either installed in a fixed position at the shore, if the object is a watercraft, or the second communication unit is installed on a boat on the water or at a platform. The second communication unit can for example be positioned near a race circuit for a sail boat race event.

According to a further advantageous embodiment of the invention the system comprises a calculating unit. The calculating unit is configured to calculate from the information received from the first communication unit a velocity of the object and a direction of movement of the object relative to the fluid. If the object is a watercraft, the velocity of the object and the direction of movement of the object relative to the water can be determined.

If the object is a fuel tank and the fluid is fuel, the movement of the fuel relative to the fixed sensor and the direction of movement of the fuel relative to the fixed sensor can be determined.

According to a further advantageous embodiment of the invention the calculating unit is considering GPS-information about the object for calculating a velocity and a direction of movement of the object relative to the fluid.

The term GPS as used within this patent application shall include any global positioning or satellite navigation system, including any appropriate kind of families of satellites, such as GPS, BDS, GLONASS, Galileo or any other satellite system. Any further advantages can be derived from the dependent claims not cited as well as from the embodiments of the invention shown in the drawings by way of example only.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, it being understood that any feature described with reference to one embodiment of the invention can be used where possible with any other embodiment and that reference numerals or letters not specifically mentioned with reference to one figure but identical to those of another refer to structure that is functionally if not structurally identical. In the accompanying drawing:

FIG. 1 is a side view of a first embodiment of the sensor of the invention incorporated in a surfboard;

FIG. 2 is a bottom view taken in the direction of arrow II of FIG. 1 of the surfboard of FIG. 1;

FIG. 3 is a large-scale section taken along line of FIG. 2;

FIG. 4 is a front perspective view of a first embodiment of a 4-blade sensor according to the invention in a perspective schematic view;

FIG. 5 is a partly exploded back perspective view of the sensor of FIG. 4 in a perspective back view according to arrow V of FIG. 4 with four strain gauges;

FIG. 6 is a large-scale view of a second embodiment of a 4-blade sensor similar to that of FIG. 4 in a different perspective and showing differently formed blades;

FIG. 7 a schematic exploded view of a third embodiment of the sensor of the invention;

FIGS. 8 and 9 show the embodiment of FIG. 7 when partly and fully assembled;

FIG. 10a is a schematic cross section through the sensor of FIG. 4 without float in a position where no forces act upon the pin so it is in its rest position;

FIG. 10b shows the sensor of FIG. 10a when a first force F is exerted upon the pin;

FIG. 10c, 10e show the sensor of FIG. 10a in further positions of the pin and the blades under action of different forces F acting in different directions onto the pin;

FIG. 11 is a schematic of an electric Wheatstone bridge circuit with embedded strain gauges;

FIG. 12 shows a fourth embodiment of the sensor according to the invention in a view like FIG. 6 with a 3-blade sensor having three unillustrated strain gauges;

FIG. 13 shows a fifth embodiment of the sensor of the invention in schematic illustration similar to FIG. 3 showing a flexible pin carrying strain gauges;

FIG. 14 is a schematic diagram illustrating an embodiment of a system according to the invention comprising an object configured as a watercraft in water and having a first communication unit, a second communication unit mounted on the shore, and a satellite;

FIG. 15 is a sixth embodiment of the sensor according to the invention in an illustration similar to FIG. 3 showing a membrane for detecting z-directional forces acting on the pin; and

FIG. 16 shows a seventh embodiment of the sensor of the invention in an illustration similar to FIG. 3 showing a membrane in the housing, near or at the blades.

SPECIFIC DESCRIPTION OF THE INVENTION

Numerous embodiments of the invention are shown in the drawings described in the following description of the figures and under reference to the drawings only in an exemplary way. For the sake of clarity identical parts or parts having identical functions have been designated with the same reference numerals, in part by adding small alphabetic characters, even for different embodiments. Features that have been disclosed only in reference to one single embodiment can, within the frame of the invention, also be provided in any other embodiment of the invention. Such embodiments are also comprised of the invention, even if such embodiments are not disclosed in the drawings.

All features disclosed in the following description are relevant to the invention. In the disclosure of this patent application there is also included the disclosure of any cited prior art documents and prior art sensor, including for the purpose to take up one or several features of those prior sensors into one or more claims of the present patent application.

An embodiment of a sensor according to the invention is designated in its entirety in the drawing with reference numeral 63. It will be referenced to in view of the object 10. The object 10 is schematically shown in the drawings as a surfboard 11. This surfboard 11 is used in a fluid 12 that in the present case is water.

According to FIGS. 1 and 2 the surfboard 11 might have a plurality of skegs 14 a, 14 b, 14 c. A middle axis of the surfboard 11 is designated with the reference numeral 15 and the direction of travel 16 of the surfboard 11 will mostly be parallel to the middle axis 15.

The sensor 63 is on the underside 64 of the surfboard 11 and is, as can be seen from FIG. 2, positioned advantageously on or near to the middle axis 15 of the surfboard 11.

FIG. 3 shows an enlarged schematic cross section view of FIG. 1 according to circle III.

The sensor 63 will be now described in detail in view of FIG. 3:

The cross section of FIG. 3 shows the inner structure of the surfboard 11 including an internal foam 19 that might be a light weight foam, for example made of polyurethane, and hard skin surfaces 20 a, 20 b that may consist of resin and glass fibers. The sensor 63 comprises a housing 21 inset into the surfboard 11 and thus fixed thereto. The housing 21 receives a ring 22 fixed to the housing 21.

Four angularly equispaced blades 25 a, 25 b, 25 c, 25 d extend radially inward from an inner face of the ring 22. The outer end 27 of each blade 25 a, 25 b, 25 c, 25 d is fixed to the ring 22. The inner ends 28 meet in a hub 65. The plurality of blades 25 a, 25 b, 25 c, 25 d form a spring 62 and lie in a common plane 73.

A pin 17 is fixed to the hub 65 of the spring 62 and is cylindrical and has a circular cross section. The pin 17 extends in a direction 74 perpendicular to the blade plane 73. The pin 17 is made of a stiff, rigid material such as metal or hard plastic and does not bend when radial forces are exerted on the pin.

FIG. 10a shows a rest position of the pin 17. The spring 62 urges the pin 17 into this rest position.

If a radial force is applied to a free end 66 of the pin 17 (see FIG. 10b ), the pin 17 will pivot from the position according to FIG. 10a into the position according to FIG. 10 b.

Since the pin 17 is rigid and stiff and will not bend, the spring blades 25 a, 25 c will bend as can be seen in comparison of FIGS. 10a and 10 b.

According to FIG. 3 the housing 21 of the sensor advantageously is closed by a cover 23. The cover 23 has a bore 24 through which a pin 17 extends.

As can be seen in FIG. 3, there is an annular space 67 between the bore 24 and the pin 17 to allow movement of the pin 17 as shown in FIGS. 10a to 10c . The bore 24 thus has an inner diameter 75 larger than the outer diameter 76 of the pin 17.

Movements shown in FIGS. 10b and 10c are for purpose of illustration only and that in real applications only very small angles, for example of much less than 1°, will be reached.

According to FIG. 5, which is an exploded view, there are four strain gauges 26 a, 26 b, 26 c, 26 d provided on the back faces 30 of the blades 25 a, 25 b, 25 c, 25 d. Other embodiments of the invention that are not shown in the drawings provide strain gauges on the front faces 29 of the blades 25 a, 25 b, 25 c, 25 d. All embodiments shown in the drawings only show strain gauges 26 a, 26 b, 26 c on the back side 30 of the blades 25 a, 25 b, 25 c, 25 d.

Strain gauges that can be employed in the embodiments of the invention are standard known electronic elements. Strain gauges appropriate for use with the invention are commercially available for example at Hottinger Baldwin Messtechnik GmbH in 64293 Darmstadt, Germany.

According to the invention strain gauges 26 a, 26 b, 26 c and 26 d are glued to the back faces 30 of the blades 25 a, 25 b, 25 c, and 25 d and then covered with an insulating material like silicone or resin. The strain gauges 26 a, 26 b, 26 c connected are via cables 34 a, 34 b (see FIG. 3) connected to other electronic elements and/or are part of an electric circuit 44 that will be explained later under reference to FIG. 11.

Strain gauges 26 a, 26 b, 26 c, and 26 d employed according to the embodiment of the invention are preferably linear strain gauges. The strain gauges that can be used within the invention change their electrical resistance if the blades 25 a, 25 b, 25 c, 25 d, on which the strain gauges 26 a, 26 b, 26 c, 26 d are glued undergo a change in length.

As can be seen in comparison of FIGS. 10a and 10b the portion of the back side 30 of blade 25 a will be elongated when the pin 17 is pivoted from the position of FIG. 10a in the position of FIG. 10b , while the length of portion of the back side 30 of the blade 25 c will shortened at the same time. This length discrepancy will lead to discrepancy in the resistance of the strain gauges 26 a, 26 c.

According to the embodiments of FIG. 3 to FIG. 10e the two strain gauges 26 a and 26 c are positioned on two blades 25 a, 25 c that are arranged exactly opposite to each other. Any change in resistance of strain gauge 26 a therefore will be the same at the opposing strain gauge 26 c, however with a negative effect.

Using an appropriate electrical circuit, these changes in resistance of the strain gauges 26 a, 26 b, 26 c, 26 d can be measured and can be used to obtain information about forces F exerted on the pin 17.

If for example according to FIG. 10b a force F is exerted on the pin 17, this will lead to a certain movement of the pin 17 that will result in a certain change in the electric resistances of the two strain gauges 26 a, 26 c.

If however a contrary force F according to FIG. 10c is exerted onto the pin 17 as shown in FIG. 10c , in the opposite direction compared to FIG. 10b , then different behavior of the deviation of the resistances of the strain gauges 26 a, 26 c will be detected.

The detection of the changes in resistance of the strain gauges 26 a, 26 b, 26 c, 26 d can be employed to derive information about the force F exerted onto the pin 17. From the information about the strength of the force F and from the direction of the force F information about the current direction D of the object 10 relative to the fluid 12 and of the velocity of the object 10 relative to the fluid 12 can also be calculated.

According to the FIGS. 10a to 10c it has been shown that detection of the change of resistance of the strain gauges 26 a and 26 c yields information about the force F acting in x-direction, or information about the part of the force F acting in x-direction can be employed. It is also possible by using the strain gauges 26 b and 26 d to obtain information about the strength of the forces F acting in y-direction. Thus, detection of the differences in the resistance of the strain gauges 26 b, 26 d can be used to derive information about the direction and the force F that have been exerted onto the pin 17 in y-direction.

According to FIGS. 1 and 2 the direction of travel 16 of the surfboard 11 is designated with an X, the direction transverse thereto is designated Y and the vertical direction is designated Z.

It shall be assumed that the strain gauges 26 a, 26 c of the sensor 63 shown in FIG. 10a are positioned in such a way at the surfboard 11 that they are lie on a line that is parallel to the direction X. If the surfboard 11 moves exactly in the direction of travel 16 through the water 13, then the force F according to FIG. 10b would be exerted onto the pin 17.

If however the surfboard 11, for whatever reason, made a reverse movement in direction X, the force F as shown in FIG. 10c would be exerted onto the pin 17 and a reverse change of resistance of the strain gauges 26 a, 26 c would be sensed.

The same applies for strain gauges 26 b and 26 d that under the previous assumption, would be oriented in this embodiment in the direction Y transverse to the direction X.

Also the changes of resistance of the strain gauges 26 b, 26 d are detected through the electric circuit 44.

From the measurements one can not only derive information about the relative speed of the object 10 relative to the fluid 12, but also information about the direction of the speed, thus indicating the direction of relative movement of the object and the fluid.

Regarding FIGS. 10d and 10 e:

Some embodiments of the sensor 63 of the invention might include a float 43 schematically shown in the embodiments of FIGS. 5, 10 b to 10 e.

This float 43 can for example be a disk and can be used to measure the buoyancy of the object 10 relative to the fluid 12 The disk float 43 can for example be on the lower free end 66 of the pin 17.

If a force is exerted on the float 43 in the direction z or in direction z as shown in FIG. 10d , then starting from the state of the sensor 63 as shown in FIG. 10a the pin 17 is drawn downward, which will lead to a change in resistance of both of the strain gauges 26 a, 26 c.

The same applies analogously if an upward (Z-direction) force F is exerted against the float 43 according to FIG. 10e that will lead to stretching of the portion of the back face 30 of the blades 25 a, 25 c again resulting in a change in resistance of the strain gauges 26 a, 26 c commonly.

While it is clear that the change in resistance of strain gauge 26 a and strain gauge 26 c according to FIG. 10d will be same or will approximately be the same, it is also clear, that the same effect will take place in a position as shown in FIG. 10e , however with a negative i.e. inverse way.

Therefore, a measurement of the change of resistance of the strain gauges 26, 26 c can also give information about whether or not a force F is exerting onto the pin 17 in z-direction or in z-direction and also information about the amount of the force F in z-direction.

Therefore, an appropriate electronic circuit 44 as shown in FIG. 11 can differ between movements of the pin 17 relative to the spring 62 in all three different directions x, y and z. This will permit receiving vector information about the direction and the length of the force vector of the force F applied to the pin 17.

For clarification it is pointed out to the fact that all embodiments shown may include a float 43 or may not include such float 43.

All embodiments of the invention as shown in the drawings can also operate without a float 43 and still permit to the user to obtain information about the forces F in x- and y-direction.

In many applications there will be no need for obtaining information about z-directional forces F. So such a float 43 can be omitted for such applications.

For further explication it is noted that the length L1 of the pin 17 and the length L2 of the pin 17 projecting from the surface 20 of the object may differ in dependency of the different conditions.

It is important for the invention that the free end 66 of the pin 17 reach a zone in the fluid 12 called the “free layer zone”.

Between the free layer zone and the surface 20 there might be a turbulent laminar zone of fluid 12 that might lead to incorrect measuring and values and results.

A turbulent zone of fluid 12 might be part of the fluid in movement due to the movement of the object and measurements within this turbulent zone of fluid might not be representative and might result in incorrect measurement values.

All strain gauges 26 a, 26 b, 26 c, 26 e are connected via cables 34 a, 34 b to further electronic components of an electronic circuit.

The circuit 44 is shown in detail only in FIG. 11. The electronic circuit may include one or more electronic elements 33 a, 33 b and/or one or more microprocessor (not shown).

According to FIG. 11 there is a power supply/voltage source 51 provided and connected to all strain gauges 26 a, 26 b, 26 c, 26 d that are in the circuit diagram symbolized by resistances.

The strain gauges 26 a and 26 b are parallel and the strain gauges 26 b and 26 d are parallel.

Further resistances R1, R2, R3 and R4 are provided.

The output voltage at the strain gauges 26 a, 26 c, that is an indication for the resistance of the strain gauges or for the change of resistance of the strain gauges, is connected to the input side of a first differential amplifier 46 a. The output of this first differential amplifier 46 a provides the first output signal 48 that gives an x-direction signal.

The strain gauges 26 b and 26 c are connected to the input of a second differential amplifier 46 b whose output corresponds to the output 49 (signal output) that is for the y-direction signal.

The output of the first differential amplifier 46 a and the output of the second differential amplifier 46 b are connected to the input of a summing amplifier 47, whose output is the output signal 50 corresponding to the signal in z-direction.

The circuit 44 as shown in FIG. 11 in total is a Wheatstone bridge. This circuit provides a very advantageous way to measure changes in resistances in the strain gauges 26 a, 26 b, 26 c, 26 d to obtain information about the strength of the force F exerted onto the pin 17 and information about the direction of the force F exerted onto the pin 17.

The measurement values obtained at the signal output 48, 49 and 50 of the three direction x, y and z can be processed using appropriate formulas and can be calculated into force information and directional information. From this information about the speed and the direction of speed of the object relative to the fluid can be calculated.

Appropriate algorithms and formulas can be employed for performing this calculation and for employing the desired information.

According to FIGS. 6, 9 a further embodiment of the sensor 63 is shown having blades 25 a, 25 b, 25 c, 25 d that are of different shape:

FIG. 6 shows blades 25 a, 25 b, 25 c, 25 d that have at their inner ends 28 a width W1 smaller than the width W2 of the blade 25 at its outer end 28.

According to FIGS. 7, 9 the sensor 63 can comprise an installation housing 35 that permits pre-installation into the object 10, for example into the surfboard 11. The installation housing 35 can comprise a compartment for receiving a sensor housing 69. The sensor housing 69 can also have a compartment 70 for receiving the ring 22 including the spring 62.

A plate 38 b can close the sensor housing 39 and can constitute the cover 23 or can be covered by a further cover not shown in the drawings.

There is a further plate 38 a shown for easy installation as well as fixing members 37 a, 37 b that facilitate mounting of the sensor.

Screw receptacles 39 a, 39 b, 39 c, 39 d serve for receiving screws (not shown) for mounting the sensor.

According to the embodiment of FIG. 12 there is 3-blade sensor 54 shown. This sensor consists of three blades 25 a, 25 b, 25 c that are arranged under an angular distance α=120°.

On the back side of the blades 25 a, 25 b, 25 c (not shown in FIG. 12) there are in total three strain gauges.

FIG. 13 discloses another embodiment showing a sensor 63 having a pin 78 that elastic or bendable. The rest position of the pin 78 is shown in solid lines and the bend position of the pin 78 is shown that is reached if a force F is exerted onto the free end 66 of the pin 78 is shown in broken lines.

Strain gauges 26 e, 26 f are indicated in FIG. 13 and provided on the outer sides 71 of the pin 78 that are capable of detecting a length change of the pin 78 due to a bending of the pin 78.

As there are several strain gauges 26 e, 26 f on the outer side 71 of the pin 78 the sensor 63 of FIG. 13 can also not only measure the velocity but also the direction of travel.

According to FIG. 1 and FIG. 14 there is also a system 72 provided that comprises not only of the sensor 63 but also a first communication unit 56. The first communication unit 56 can be an integral part of the sensor 63 or can be a separate part on the object 10 and being connected to the sensor 63 either by cable or via wireless connection.

The first communication unit 56 can interact via a signal path 59 a in a wireless manner with a second communication unit 57 on a distant place. The second communication unit 57 can be arranged on land or alternatively on a platform on the sea or on another moving object.

All measurement information obtained from the electronic circuit 44 can be transmitted via the first communication 56 to the second communication unit 57.

According to a further embodiment of the invention it is also possible to include GPS data.

FIG. 14 discloses a system 72 that may also comprise a satellite 58 that is via a signal path 59 b, which can be unidirectional, capable of transmitting GPS data to the first communication unit 56. This GPS data can be used or employed or transmitted by the first communication unit 56 to the second communication unit 57.

The second communication unit 57 can be connected to a calculating unit 60 that can calculate all received data. From the data received by the calculating unit 60 information about the relative movement of the object 10 relative to the fluid 12 in x-, y- and/or z-direction can be obtained.

For purpose of clarification it shall be noted that the calculator 60 can also be installed at the object 10, and can also be integral part of the sensor 63 or a separate part of the sensor 63.

While the previous embodiments employ—in part—a float 43, instead of such a float a membrane 61 can be used.

The membrane 61 can be for example positioned at the free end 66 of the pin 17 (see FIG. 15) or can be positioned within the housing 69.

The membrane 61 can be used to obtain buoyant information by sensing pressure or by sensing changes in pressure.

Instead of a membrane 61 any other pressure sensitive sensor or detector can be employed that might generate for the system 72 information about a relative direction of the object 10 relative to the fluid 12 in z-direction. 

1. A sensor for measuring movement of an object relative to a fluid, the sensor comprising: a housing fixed to a surface of the object; a spring on the housing formed by a plurality of blades each having an outer end fixed to the housing and an inner end connecting to a hub, the plurality of blades defining a plane; respective strain gauges on the blades; and a rigid pin mounted on the hub of the spring and extending in a direction generally perpendicular to the plane and projecting from the surface of the object and into the fluid.
 2. The sensor according to claim 1, wherein the plurality of blades comprises at least three blades.
 3. The sensor according to claim 1, wherein the blades are arranged angularly equidistant from each other relative to an axis of the hub.
 4. The sensor according to claim 1, wherein the plurality of strain gauges comprises at least three strain gauges positioned on three different blades.
 5. The sensor according to claim 1, wherein the pin carries a float.
 6. The sensor according to claim 1, wherein the housing comprises a cover flush to the surface of the object.
 7. The sensor according to claim 6, wherein the cover has a bore through which the pin extends and having an inner diameter larger than an outer diameter of the pin.
 8. The sensor according to claim 1, wherein the spring assumes a rest position for the pin when no forces act upon the pin.
 9. A sensor for measuring movement of an object relative to a fluid, the sensor comprising: a housing fixed to a surface of the object; a base fixed to the housing and defining a plane; am elastically deformable pin mounted of the base, extending generally perpendicular to the plane, and projecting from the surface of the object into the fluid; and a plurality of strain gauges on the pin.
 10. A system for determining information about a movement of an object relative to a fluid, the system comprising: a sensor as defined in claim 1, a first communication unit on the object and connected to the sensor, and a second communication unit receiving information from the first communication unit.
 11. The system according to claim 10, further comprising: a calculating unit configured to calculate from information received from the strain gauges of the sensor a velocity of the object and a direction of movement of the object relative to the fluid.
 12. The system according to claim 11, wherein the calculating unit uses GPS-information about the object for calculating a velocity of the object and a direction of movement of the object relative to the fluid. 